Anesthesia has traditionally meant the condition of having the perception of pain and other sensations blocked. This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience.
The anesthetic qualities of nitrous oxide (isolated in 1773 by Joseph Priestley) were discovered by the British chemist Humphrey Davy about 1799 when he was an assistant to Thomas Beddoes, and reported in a paper in 1800. But initially the medical uses of this so-called “laughing gas” were limited—its main role was in entertainment. It was used on 30 Sep. 1846 for painless tooth extraction upon patient Eben Frost by American dentist William Thomas Green Morton.
Forms of dental anesthesia are similar to general medical anesthesia except for the use of nitrous oxide, relatively uncommon outside of the dental field in the U.S. Nitrous oxide (N2O), also known as “laughing gas”, binds to the hemoglobin in the lungs, where it travels to the brain, leaving a disassociated and euphoric feeling for most patients. N2O is typically used in conjunction with Procaine.
In Policy on Minimizing Occupational Health Hazards Associated With Nitrous Oxide The American Academy of Pediatric Dentistry (AAPD) recommends that exposure to ambient nitrous oxide be minimized to reduce occupational health hazards associated with nitrous oxide.
Collection of ambient nitrous oxide involves 2 separate mechanisms. The first, the scavenging system, is part of the nitrous oxide delivery system. It begins at the nitrous oxide tanks and terminates at the expiratory valve in the mask. Canadian studies in hospital settings have shown that frequent and regular inspection and maintenance of the nitrous oxide delivery system, together with the use of a scavenging system, can reduce ambient nitrous oxide significantly.
Another reason for providing gas scavenging apparatus is to scavenge aerosols and splatter (air-entrained liquids) which are believed to spread infections among dental personnel.
In the dental environment, patient behaviors such as talking, crying, and moving have been shown to result in significant increases in baseline ambient nitrous oxide levels despite the use of the mask-type scavenging systems. By using a well-fitted mask and an appropriate amount of suction via the scavenging system, the increased pressure on the patient's face by the mask will reduce leakage.
NIOSH (National Institute for Occupational Safety and Health) has recommended an oral evacuation rate of 45 L/min for maximizing scavenger effectiveness. However, scavenging at this rate has been shown to reduce the level of psychosedation achieved with nitrous oxide inhalation.
The second mechanism, the “exhaust system”, collects escaped nitrous oxide and includes two entities. First, an appropriate non-recirculating ventilation system is recommended by NIOSH to provide continuous rapid air exchange. It is important to vent waste gases outside of the building and away from fresh air intakes.
Second, a high-volume aspirator, placed near or within 20 cm of the patient's mouth, has been shown to reduce significantly ambient nitrous oxide levels in the dental environment.
Diligent use of these two mechanisms in the pediatric dental environment has allowed for the reduction of ambient nitrous oxide to the levels recommended by NIOSH.
The AAPD recommends that dentists and dental auxiliaries minimize their exposure to nitrous oxide by maintaining the lowest practical levels in the dental environment. Adherence to the recommendations below can help minimize occupational exposure to nitrous oxide.
1. Scavenging systems must be used when nitrous oxide is employed.
2. Exhaust systems that adequately vent scavenged air and gases to the outside of the building and away from fresh air intake vents should be employed.
3. Careful, regular surveillance and maintenance of the nitrous oxide/oxygen delivery equipment must be practiced.
4. Mask size should be such as to ensure proper fit for each patient.
5. Nitrous oxide discharge from the oral cavity of the patient should be minimized during dental procedures.
Various patents describe method and apparatus for administering anesthesia gas and scavenging waste gases, as exemplified by the following.
U.S. Pat. No. 4,151,843 (“843 patent”) discloses apparatus for administration of a gas to a human and the exhausting thereof. An apparatus for administration of a gas to a human and the exhausting thereof including a gas flow control connected to one end of a gas administering device which has on the other end protrusions for sealing engagement with nostrils of the nose. A gas supply conduit is connected to the gas flow control and a gas exhaust conduit is connected to the gas flow control, the gas flow control causes an intake of gas through the supply conduit and said gas administering device and out said protrusions thereon upon inhalation of a user of the apparatus. The gas flow control causes the exhausting of exhaust gas from said gas administering device through said gas flow control and out said gas exhaust conduit to a gas collector upon expiration of the user of the apparatus. The gas flow control causes the flow of fresh gas through a supply conduit to be blocked during user expiration.
In the 843 patent, a fairly small nose cap seals against nostrils and channels gas into the nostrils during inhalation and vacuums exhalation from the nostrils (only) through the same nose seal. Also exhausts gas that may leak from seal against nostrils. Hoses pass around both sides of head but elevated above eye level. The device only scavenges from inside the mask (the patient's nose), not the mouth. The routing of hoses on both sides of the mask may impair access by the doctor.
U.S. Pat. No. 5,513,632 (“632 patent”) discloses ventilation of medical gases. A downdraft system is used for withdrawing and collecting medical gases, fumes, mists and particulates from the vicinity of a patient's face. Two intakes are located on respective sides of the patient's face, at the cheeks. The intakes extend from temple to chin. They are connected through a ducting system to a source of vacuum for collecting the medical gases. The ducting system is configured to allow the adjustment of the intake positions. The intakes create a flow of air across the patient's face from above the nose to below the mouth so that gases leaking during administration of gases or exhaled by the patient, and fumes, mists or low velocity particulates generated, for example, in orthodontic procedures are captured in the flow across the patient's face into the intakes. This leaves the patient's mouth and nose fully exposed and unobstructed by the gas evacuation apparatus so that the administration of gases, dental treatments and any other procedures requiring access to the mouth and nose area may be carried out.
In the 632 patent, scavenging intakes are provided in the facial area without a nose-enclosing mask. This device does not supply an anesthetic gas to the patient.
U.S. Pat. No. 4,770,169 (“169 patent”) discloses an anesthetic scavenging face mask having a scavenging channel running along the perimeter of the mask. The mask is provided with an anesthetic gas inlet and a vacuum outlet. The scavenging channel is connected to the vacuum outlet.
In the 169 patent, only gases exhaled from the patient's nose are exhausted, and hoses coming out of both sides of the mask may impair access to the patient's mouth by a dentist.
U.S. Pat. No. 4,248,218 (“218 patent”) discloses a scavenging mask apparatus for administering gas to a patient, the apparatus comprising a nasal cannula for delivering gas to the patient's nostrils, a tube connecting the cannula to a source of gas, a nosepiece adapted to fit over the nose and cannula, and a tube connecting the nosepiece to a source of vacuum. Gas exhaled through the patient's nostrils or escaping from the cannula is scavenged by the air flow in the nosepiece, thereby minimizing loss of gas to the environment. The nosepiece is also provided with a plurality of holes in the underside thereof to scavenge gas exhaled through the patient's mouth.
In the 218 patent, the mask has hoses coming out of both sides, which can impair access to the patient's mouth, by the dentist. Furthermore, the bulky nosepiece may itself impair access to the mouth and vision of the lower quadrant. The holes in the underside are not likely to be very effective since the holes are spread out over a wide area not targeted for creating laminar flow up from the mouth.
U.S. Pat. No. 5,715,813 (“813 patent”) discloses capture system for waste anesthetic gas. A waste anesthesia capture system includes exhaust apparatus having a rate of fluid flow of at least five times the rate of anesthesia gas delivered to a patient, the exhaust apparatus having a capacity of at least ten cubic feet per minute. The system further includes an exhaust conduit in fluid-integral communication, at a first opening, with the exhaust apparatus. Also included is a Y-shaped anesthesia gas conduct formed of a flexible memory-retaining material. A cross-section of a base portion of that conduit has an output in fluid-integral communication with a second opening of the exhaust conduit, and each of two branches of the Y-shaped conduit define longitudinal axes, the axes having a selectable separation in the range of nine inches to two feet, and each open end of the branches defining a diameter in the range of 0.5 to 4.0 inches.
In the 813 patent, large round intake tubes for scavenging gas are positioned on either side of the neck. These appear to be bulky, likely to get in the way of a dentist, and difficult to position. A separate mask supplies nitrous oxide. The bulky nosepiece also obstructs vision to the lower quadrant of the mouth.
U.S. Pat. No. 5,636,627 (“627 patent”) discloses equipment and method for gas extraction in general anesthesia. Contaminated air in general anesthesia is extracted via a hemispherical hood 1 located closely over the patient. The hood 1, which is of a thin-wall transparent-shell form, is mounted for hand-touch variation of its orientation on an arm 2 which is carried by a telescopic column 3 that allows for height adjustment. The arm 2 extends from a unit 18 that allows the hood 1 to be swung horizontally about the column 3, and gas is drawn from the hood 1 near its open mouth 6 via a low-down port 7 (FIGS. 3 to 5) that is coupled through the arm 2 and column 3 to a fan unit 4. Relief 23 of the bottom margin of the hood 1 may be used to enhance access to the patient, and for maneuverability the column 3 is trolley-mounted or adjustable laterally on a fixed track 35 (FIGS. 9 and 10).
The 627 patent addresses equipment and method for gas extraction in general anesthesia. A lightweight, transparent hemispherical hood is positioned over the patient's face. The hood evacuates escaped/exhaled gases. The hood is quite large, and would appear likely to interfere with any work not done at arm's length. The equipment only scavenges, it does not supply the nitrous oxide to the patient.
U.S. Pat. No. 5,195,512 (“512 patent”) discloses apparatus for evacuating excess gases from surgery patient's face. An apparatus for removing introduced or exhaled from the mouth and nose area of a patient via a suction device is disclosed. The apparatus includes a first flexible and hollow cylinder having one closed end and one open end and a plurality of small openings grouped together in a central portion of the first cylinder. The open end is attachable to the suction device. The second flexible and hollow cylinder is attachable to the operating table for supporting the first cylinder. A flexible tube extends through the second cylinder to provide rigidity and malleability to the second cylinder. The first cylinder is coupled to the second cylinder.
In the 512 patent, an exhaust hose is suspended over the nose/mouth area of patient by positionable tubing attached to the exhaust hose. The exhaust hose has several small evacuation holes. The exhaust hose is clamped to an operating table, and the mounting system would appear to be inappropriate for use in dentistry. The device only scavenges, it does not supply nitrous oxide to the patient.
U.S. Pat. No. 3,537,447 (“447 patent”) discloses medical shielding structure. A shielding apparatus of a medical operating area which forms a protective air shield between, for example, a dentist and his patient. The shielding apparatus includes a longitudinally extending outlet header having a discharge opening therethrough effective to discharge air in a planar-laminar flow path. Air is supplied to the outlet header by a motor driven blower through a conduit system. An inlet structure is spaced from the outlet header ad receives the shielding airstream. The outlet header and the intake structure are mounted on an articulating support arm. Conduit means lead from the intake structure and I the preferred embodiment, discharge contaminated air passing therethrough to a filter. A portion o the filtered air is recalculated to the outlet header and another portion is exhausted.
The device of the 447 patent provides a “blanket of air”, a substantially flat airflow across a field for entraining and collecting exhaled gases, generally from the mouth, using an air supply manifold and a matching scavenging manifold placed on either side of the face. No provision is made for supplying nitrous oxide to the patient.
As evidenced by the patents referenced above, nitrous oxide anesthesia is typically administered by way of mask over nose, and safety regulations say that mask must also collect (vacuum up) anesthesia gas that the patient exhales. These references generally show complicated masks that, in some cases protrude substantially from the patient's face and/or cover the patient's top lip. This obstructs dentist's view and access with tools, plus makes operating under the patient's top lip quite difficult.
Also, the prior art in the patents referenced above generally has the mask's in and out hoses going both ways around head and the two hoses have a slide clasp that is cinched up behind the head and/or the headrest to hold the mask on. Problems with this include interference with turning patients head, and the raised hose on cheek gets in way of dentist.
The “Safe Sedate” Dental Mask System, by Airgas Puritan Medical, is similar to some of the patent references above in that it is a dental mask fitting over (around) the patient's nose. The system relies on precise administration of the anesthetic gas to meet government compliance regulations. The system also evacuates gas that is not inhaled, but doesn't evacuate (scavenge) exhaled gas from the mouth.
The typical mask system, as shown in “Safe Sedate” and some of the patents, comprise a cup shaped element that fits over the patient's nose, somewhat like a smaller version of a traditional oxygen mask (which, albeit, usually encompasses both the nose and mouth). It is sometimes difficult to get a tight seal between the mask and the face, without exerting undue (uncomfortable) pressure on the mask. Additionally, it can be somewhat uncomfortable for the patient to wear.
Providing a system that delivers and scavenges anesthetic gas to a patient, without impairing access to the patient's mouth by a dentist, remains a challenge. What is needed is a more ergonomic design, addressing some of the shortcomings of the prior art, as noted above.